Fix cancellation token race during parser comparison (#4280)

src/Runner.Worker/ExecutionContext.cs

@@ -77,8 +77,7 @@ namespace GitHub.Runner.Worker
 
         List<string> StepEnvironmentOverrides { get; }
 
-        ExecutionContext Root { get; }
-        ExecutionContext Parent { get; }
+        IExecutionContext Root { get; }
 
         // Initialize
         void InitializeJob(Pipelines.AgentJobRequestMessage message, CancellationToken token);
@@ -251,7 +250,9 @@ namespace GitHub.Runner.Worker
             }
         }
 
-        public ExecutionContext Root
+        IExecutionContext IExecutionContext.Root => Root;
+
+        private ExecutionContext Root
         {
             get
             {
@@ -266,13 +267,7 @@ namespace GitHub.Runner.Worker
             }
         }
 
-        public ExecutionContext Parent
-        {
-            get
-            {
-                return _parentExecutionContext;
-            }
-        }
+
 
         public JobContext JobContext
         {

src/Runner.Worker/PipelineTemplateEvaluatorWrapper.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Threading;
 using GitHub.Actions.WorkflowParser;
 using GitHub.DistributedTask.Expressions2;
 using GitHub.DistributedTask.ObjectTemplating.Tokens;
@@ -226,8 +227,12 @@ namespace GitHub.Runner.Worker
             Func<TNew> newEvaluator,
             Func<TLegacy, TNew, bool> resultComparer)
         {
-            // Capture cancellation state before evaluation
-            var cancellationRequestedBefore = _context.CancellationToken.IsCancellationRequested;
+            // Use the root (job-level) cancellation token to detect cancellation race conditions.
+            // The step-level token only fires on step timeout, not on job cancellation.
+            // Job cancellation mutates JobContext.Status which expression functions read,
+            // so we need the root token to properly detect cancellation between evaluator runs.
+            var rootCancellationToken = _context.Root?.CancellationToken ?? CancellationToken.None;
+            var cancellationRequestedBefore = rootCancellationToken.IsCancellationRequested;
 
             // Legacy evaluator
             var legacyException = default(Exception);
@@ -261,7 +266,7 @@ namespace GitHub.Runner.Worker
                 }
 
                 // Capture cancellation state after evaluation
-                var cancellationRequestedAfter = _context.CancellationToken.IsCancellationRequested;
+                var cancellationRequestedAfter = rootCancellationToken.IsCancellationRequested;
 
                 // Compare results or exceptions
                 bool hasMismatch = false;